1. Field of the Invention
The present invention relates to an anticorrosive and antifouling additive for paints, which is effective to protect structures made of steels or ferrous materials such as steel ships and pipes from rust, and prevent the adhesion of organisms and algae to the structures used in the presence of seawater or fresh water, and also a paint containing the same additive.
2. Disclosure of the Prior Art
In the past, antifouling paints have been used to prevent the adhesion of organisms such as barnacles, seashells, marine algae or the like to ships and structures used in the presence of seawater or fresh water. In general, it is believed that macro fouling or bio-film that is called slime such as bacteria, floating organic substances and diatom is firstly formed on the ship bottom, and then the adhesion of various kinds of marine organisms occurs. Currently, the following antifouling paints (1) to (3) are mainly used to prevent the adhesion of marine organisms.
(1) Hydrolysis Type Paint (Self-Abrasion Type Paint)
This paint is known as a kind of dissoluble matrix type paint. When an applied film of this paint comes into contact with seawater having a pH value of 8.0 to 8.2 that is slightly alkaline, hydrolysis proceeds at a constant speed, so that a resin of the surface dissolves, and a new surface of the applied film appears. A sterilizing force of copper ions eluted from the surface of this applied film prevents the adhesion of marine organisms. In brief, the applied film having a multilayer structure of the paint containing an antifouling agent is formed on the ship bottom, and the layers of the applied film peel off on a one-by-one basis in seawater to prevent the adhesion of marine organisms.
(2) Hydration-Dissolution Type Paint (Hydration-Decomposition Type Paint, Hydration-Decay Type Paint)
This paint is a kind of dissoluble matrix type paint as well as the hydrolysis type paint described above, and is characterized by comprising a polymer, copper suboxide and a rosin extracted from pines as the main components. The rosin is a natural oligomer composed of abietic acid having a molecular weight of about 300 and an isomer thereof. Affinity for seawater and the slight dissolubility thereto of the rosin are known for a long time. When an applied film of this paint comes into contact with seawater, a surface portion of the applied film slightly dissolves due to the dissolubility of rosin, and agents such as copper suboxide appear on the applied film. In brief, since the surface of this applied film is normally slimy, the adhesion of marine organisms can be prevented by synergistic effects of the above agents and the surface condition that the marine organisms are difficult to adhere.
(3) Extraction Type Paint
This paint is known as a kind of indissoluble matrix type paint, which comprises copper suboxide, rosin and a hydrophobic synthetic resin as the main components. Although this paint itself is not dissolved, only an antifouling agent included therein elutes from the matrix into seawater. In comparison with the dissoluble matrix type paint described above, it is characterized in that a larger amount of the agents is included in the paint, and the applied film has an increased hardness.
Thus, most of the ship bottom paints utilize the sterilizing force of copper ions. When some conditions such as seawater temperature, marine environment and cruising conditions of ships are satisfied, the effect of preventing the adhesion of marine organisms can be achieved to some extent. However, it is desired to further improve the effect of preventing the adhesion of marine organisms such as barnacles, seashells, marine algae or the like.
The ships of steels or ferrous materials also need to be painted two to four times with anticorrosive paints to prevent the occurrence of rust when the ship bottom comes into contact with seawater for a long time period. Most of the anticorrosive paints of the past usually contain organic tin polymer compounds to prevent the adhesion of marine organisms. Since the organic tin polymer compounds are materials having high bioactivity, they have detrimental effects on another marine organisms other than barnacles, seashells, and marine algae, e.g., the occurrence of deformed fishes. For this reason, the use of the organic tin polymer compounds has been voluntarily restrained since the latter half of the '80s.
In addition, as a consequence of the consultation held at the International Maritime Organization (IMO) headquartered in London from Jun. 28 to Jul. 2, 1999, agreements of prohibiting the use of the organic tin polymer compounds for the ship bottom paints by the year 2003 and the use of them in all aspects by the year 2008 were made. However, at present, since there is no paint or additive for effectively preventing the adhesion of marine organisms, which takes the place of the paints containing the organic tin polymer compounds, the development of such paint and/or additive is urgently necessary.
From the above reasons, paint makers of most of the industrialized countries have stopped the use of the organic tin polymer compounds. Under present circumstances, since the adhesion of marine organisms can not be sufficiently prevented, there is a problem that the frequency of cleaning the marine organisms adhered on the ship bottom increases, and the cost of the cleaning operation rises.
The adhesion of marine organisms wields a very large influence over ship service. In usual painting operation for the ship bottom, an anticorrosive treatment (primer treatment) is performed several times to the metal portions, and then a ship bottom paint is applied. It is said that the load on the engine increases with increase in thickness of the applied layer. For example, when only 5 .mu.m increases in thickness of the applied layer, about 1 knot drops in speed of the ship. In this case, when barnacles or seashells attach the ship bottom, the resistance to seawater further increases, so that 3 to 5 knots drop in speed of the ship.
Thus, since the fuel efficiency of the ship becomes poor, it is necessary to perform the cleaning operation of the adhered marine organisms and then the repainting operation every 3 months or every 6 months, with respect to small fishing boats. Consequently, much effort and cost are expended on the regular maintenance of the fishing boats. On the other hand, with respect to large ships such as tankers, there is a problem that a breakage of camshaft is caused when large amounts of the barnacles or seashells adhere under a marine environment, and the load on the engine excessively increases.
On the other hand, in plants using seawater to cool the driving system, there is another problem that the intake amount decreases due to the adhesion of marine organisms to piping, so that seizing up of the driving system is caused by a reduction in cooling efficiency.